It is generally well known that resistor networks offer significant advantages over the use of discrete components. For example, resistor networks provide substantial reductions in board space, improved reliability by providing reduced numbers of solder joints, and improved temperature performance in terms of temperature coefficient tracking.
Such advantages are especially realized with well known semiconductor ladder-resistor networks. Ladder networks are typically fabricated using a primary arm made of semiconductor material which is interrupted in its longitudinal direction by metal contact areas according to the desired resistor ratio and in order to form corresponding series resistors. To each of these metal contact areas, a respective shunt arm of semiconductor material is connected via a respective metal interconnection to form shunt resistors. The metal contact areas within the primary arm cause undesirable, sometimes even non-ohmic, contact resistances which are in series with the actual series resistors of the primary arm and falsify the values of the series resistors. A specific problem arises from the fact that from a production point of view, these contact resistances are unstable, so that the exact value of the contact resistance varies and is not predeterminable. Furthermore, because of the contact resistances, the actual desired series resistance cannot be made arbitrarily small, because the total resistance is always at least as high as twice the contact resistance. Corresponding contact resistances, and the above-described problems associated therewith, also occur at the metal interconnections between the primary arm and the shunt arms.
It is, therefore, an object of the present invention to provide an improved semiconductor ladder-resistor network structure in which the effect of parasitic resistances is substantially reduced over the above described prior art structures.